1. Field of the Invention
The invention relates to novel devices for delivering radio frequency energy (RF), for example during tissue ablation procedures.
The invention relates in particular to a novel concept of an electrode for the optimization of radio frequency ablation. This concept will hereunder be nominated as the cooled-wet electrode.
2. Description of the Prior Art
Although surgical resection is still considered as a primary option for the treatment of malignant tumors, minimally invasive alternatives including intraoperative cryosurgery, local injection of ethanol, microwaves, interstitial laser therapy focused ultrasound and radio frequency (RF) tissue ablation have been developed in order to ablate the tumor less invasively for the safety of the patient and reduction of the costs and/or to broaden our capability in treatment of the patient.
Among these approaches, RF ablation has shown the greatest impact on recent experimental and clinical research because of its low invasiveness, simplicity and favorable cost-effectiveness.
In RF ablation the radio-frequency waves are emitted from a generator through an uninsulated part of the electrode which is inserted into a target tissue. The tissue destruction in a form of coagulation necrosis is caused primarily by resistive heating in the surrounding tissue and secondarily by the peripheral passive heat conduction.
Resistive heating is proportional to the square of the distance between the central electrode and adjacent tissue. Therefore, significant resistive heating only occurs within a rim of tissue in direct contact with the electrode. Beyond this rim, the tissue is further heated as a result of passive conduction of increased temperature. However, the RF emission is readily terminated as a result of impedance rise at the electrode-tissue interface, which is secondary to tissue desiccation and carbonization. Due to such non-optimal RF energy delivery and dissipation, the lesion size induced by known prototypes electrodes is smaller than 2 cm, which is obviously insufficient for tumor ablation. Similar to the principle in surgical resection, the ideal range of RF tissue destruction should involve the entire tumor and a layer of adjacent normal tissue as a safety margin to avoid incomplete ablation.
Many known technical innovations have been made to increase the lesion size in RF ablation. These include the introductions of:
1) bipolar electrodes;
2) a cooled electrode and cooled-clustered electrodes;
3) a xe2x80x9cwetxe2x80x9d electrode with hypertonic saline infusion; and
4) an expandable electrode.
According to the principle of minimal invasiveness, a monopolar is preferred to multipolar electrode.
As shown in table 1, although markedly increased, the lesion sizes induced by these modified devices are still limited, normally less than 4 cm in diameter. If a tumor larger than 2 cm, there is little chance to achieve complete ablation by a single session. Therefore there is still a demand to further optimize these devices and techniques.
Table 1 shows the lesion sizes induced by different known designs of electrode in RF Ablation.
The main object of the invention is to provide new device and methods yielding good RF ablation results and providing larger lesion size. In particular whereby the lesion size is larger than 5 and preferably more than 6 cm.
According to the invention this is realized by a combination of separately known features, which in combination surprisingly results in a more effective RF ablation. This is realized by an increased conductivity of the target tissue as well as at the electrode tissue interface in relation to a decreased tip temperature.
The invention therefore provides a device for delivering radio-frequency energy combining the characteristics of a xe2x80x9cwetxe2x80x9d electrode and of a cooled electrode.
A main object is a minimal invasiveness of the radio-frequency ablation technique. A minimal invasiveness is obtained by a precise puncturing and guidance towards the tissue to be treated. It is therefore a further object of the invention to improve the efficiency of the puncturing and guidance of the radio-frequency electrode and more broadly of all instruments used in RF ablation. The puncturing is presently performed by the sharpened distal end of the electrode. As this distal end is often open introduction sometimes causes obstruction and once introduced blocks off these openings at the distal tip. It will be understood that the use of guidance means is not necessary for the use of the cooled wet electrode. The puncturing can be performed by the sharpened distal end of the cooled wet electrode as sole puncturing mean.
As a solution to this disadvantage the invention provides further a separate guidance element for the guidance of an instrument, in particular a radio-frequency electrode. The guidance element according to the invention is substantially formed by a open hollow shaft having a cylindrical central bore which is adapted in dimensions for the temporarily housing and axial displacement of an instrument during radio-frequency ablation procedures. Said instrument-can be for example a puncturing needle for a smooth introduction towards the tissue to be treated, a radio-frequency electrode for the radio-frequency ablation step and further a biopsy needle or biopsy clamp for providing proof of the efficiency of the radio-frequency ablation procedure by the collection of a tissue sample.
It will be understood that several cooled wet electrodes, for example two, three, four or more can be used as a clustered cooled wet electrode device when the tumor to be treated is of an excessive dimension.